Signal collecting system



July 27, 1943- w. A. SCHAPER SIGNAL COLLECTING SYSTEM Filed March 8,1941 INVENTOR. lV/LL/HM/Z SCHflPE/Q.

Patented July 2751943 tion of Illinois This invention. relates to signalcollecting sys terns for radio receivers and particularly to signalcollecting systems :of the type that employ an "exposed, inductiveelement commonly called aloop.. .1

Aloopconsists generally of a number of turns of (wire mounted upon aframework of insulating material and-its two-ends' are usually connectedwith a'condenseij-to-form a resonant circuitwhich is commonly-called theloop circuit. :11? aloop circuit is tuned to resonance with adesiredsignal f the; intercepted voltage ismaterially increased. Loopcircuitsthereioreinclude usually a variable condenser or avariableinductance in orderthat they maybe tuned over a desiredrange-otfrequenciest 1 I ."--The present invention relates toinductively William A. Schaper, Cicero, Ill., assignorto l'loh sonLaboratories, Inc., Chicago, Ill.',a corplo'r Application-March 8, 1941,Serial l lo.-

; I 1:? ioiaims. (cipzso g mj Therefore, to prevent the loop fromreducing the tuning range f obtained 'bel'ow an essential minimum 'itis' necessaryjtd, restrict itsiinductance, that is, to keep the numberof its turnsk'at a minimum and-etc m'ake it small in size. Howeven' -thesignal eiiergyrintercepted by 'a loop is directly proportionalto thenumber and size of its turns.:i Additionally; ,itxj inherently decreaseswith'iidecreasi'ng 'l frequency; therefore the loop must be of adequatesize and have an adequate numberef turns- 1r. -satisiai'ztoryi receptionand satisfactory performance Qfs'the' receiver .is

had over the total'tuningirange.: i a

- It is' 'an olojectof the present invention providea'movabler-coreetuned signal collecting systemof theztype employinganexposed inductive tuned loop antenna systemsemploying variableinductors of the movable core type.

- Tuning by the relative movement of a co'l and a magnetic core, is nowgenerally known. Over other tuning devices the movable .core inductoroffers the advantage of compactness and durability and it allows theperformance ofthe circuit which it tunes to be predetermined within widelimits Therange-of-inductahce variation 0btcinable with a movable coreinductor is deter- {ni'ned by the efiectiv epermeability ofjit's core.The permeability of cores-intended for highfrequency operation, however,is limited by the iact that the magnetic material from which they arernade must be finely subdividedand, the resultelement, and whichcoversan adequate range of frequencies; a; 1;

: Additionally it isran object of. the present invention to providea',=movable-core-tuned signal 7 collecting xsystem'remploying a loop andcombinant {particles carefully insulated to impede the formation of eddycurrents in the core and this severely reduces the permeabilityinitially possessed by the magnetic materials fromwhich the 7 coresare-made. The; effective permeabilities which the art has been abletorealize in high frequencycores without excessive eddy current lossesare of the order offlO to 15; they are more than adequateto tune highfrequency circuits over wide ranges of frequencies such as thebroadcastrange. 1

However, when a loop circuitis tuned by a ,-movable,core variometer. the1oop,.which forms part of the totallinductancewoi the system but whichis removed irom the effect of the tuning core materially reduces therange of inductance :variationobtainable withinthe' circuit; and-thelarger the loop and thegreater the number of -lecting .system--for-.radio receivers and thelike .and of the type employingan; exposedinductive its turns the more pronounced will be this range reducingeffect until the'permeabilities now: avail- -able are no 3 longeradequate to" tune the loop ,systemover asufiiciently wide range offrequencies, such as for instance the broadcast-band.

ing adequatetuning. range with adequate signal interception overtheuwhole of. saidyrange. 1 :It isxanot-her objectof the presentinvention to provide a loop-systemoflthetype tunedby movable coreinductors and covering a widerange of frequencies while maintaining thesignal voltage supplied";tolthexgrid of the first tube-independent offrequency. I

,.-=Additionally ;it is anxobject-of the present invention:tO'npIQVidega/ loop system of the type tunedaby movable core inductorswhich, while providing, for adequate signal interception, isoapable-rofgbeing tuned overa wide'range'of frequencies withthessignalyoltage supplied to the grid of l the: first-- tube beingindependent of frequency: q

' The presentinvention furnishes a signal 001- element, which includesan unexposed inductive element/comprising a-winding nd a core structure,said core-nstructure having. a conductive vention said 'core portionsmay be given such proportion as the signal energyf'ihtercepteg'fby.

made o'fcornniinutedmagn'eticmaterial: sucni as vary the inductance ofsaid winding to change 5 the resonant frequency of the system theysimultaneously vary the resistance of said winding in such aminnerthatt-he ratio R of the system varies substantially inversely as thefrequency In this manner mT-gaim Ofth'ej" "*range of inductancevariation than can be realsignal collecting circuit increases in thesame the exposed inductive element'dec'reas'esiwith'the" result that thevoltage supplied to the grid of the first tube remains indepentliiii of'frequencyi over the total frequency range covered and is. proportionalonly to the strength of the signal'receivedr 1 5 In"- the accompanyingdraw lngtr preferred em-r bodmient of the I presentinvention i isexplaincd by wayl'oi -examples 5: i Fig". 1* shows the wiringi; diagramof-qa signal collecting system:embodyingeflteipresentiinvention; and 7 Y1;; Fig. 2- sh'o ws an enlarged I sectional-L viewrofi the movable coreinductor-'- employedi in ther system 831. j .i The' 'signalcollecting-system ofl xFig. l zcomprises aio'op' I ,a movabie coreinductor tandcmd'enser 5 connected to form ae seriesresonantcircuit,"one endot saidloop and-'jon'e-zelectrode; or saidt-co'ndenser bein'g'cQn-necteditogmundp Movable core iiiducstor 2conststs' oi'arwindingijanti a core stricture 4; movable relatively to said winding tovary its inductance and to thus time theccir can" over: an rangecrfrequenciessjj 'r-n incomsigh'alis interceptewbyt loop" I; is:amplified ifi sries resonant circult l'gslmndaS; and therr'ese ona'ntpotential developed across condansen 5 ;is applied to grid 0 or vacumntube l; the:..junction between inductor 2 and ccndenser 5 being connectddirectlyto"slld gridl' e witl'i 'refreiice to"- Fig; zdnmicto 8 "Winding3 wound Moon 0011 fdmn 8101* insulating materialand having a lengthseveral times" its diameter. Within coil form ltlie're 'i's movablyrdu'ghlyto the lengthof winding'm "An opera't iiig handle 9 *oi nonmagnetic-material isprtivided a't one endoftli'e core structure:iPoi'tionwwis iron or ironalloytlie individual partlcles otswhich havebeen insulated from one another and have 'tieen compounded undrprom'eintoaoore body of predetermined 'sha'pe' and permeability; coresof this ftv'p'e' are -wei1 -known -in the art and are, for instance,disclosed in='Uriited States Patent 6 li fifi twpfjlydbl'bfl'l "Cdlpdifibfl lb-is made 01 a conductive material such: as copperaluminum orbrass 1 and nas -prerrably' the shape of pressinguninsulatedmet-a1owdere mto a body 6 stanoe-bytliemctai tube-'or coreportlonwli being 7trated in: the -drawing; that is;'.whentits conduc- 'tiveportion-lbzisicompletely within windingvl the inductance of inductor 2is at its minimum 7 5 :mum inductance.

iaedbv the use of a magnetic core portion alone. 5For-ins tance; if theeffective permeability of the magnetic-core portion relative to theparticular winding shown isll, and if theconductive core portion"isbonstrubted to reduce the inductance of w-inding 3 to one third of itsvalue in air, the 0 inductance of the device changes from L/3 to 11L";'thatis, the'devic'e provides an inductance change of a ratio'of 33. I lv Reverting now to Fig. 1 the inducta'nceofldop l-restrictstheinductance variation produced by 5 movable core inductor 2 in circuit l,'2 a'nd 5 ini'the same manner as an'yj-Iotherseries conn cted-coil'offixed inductance value: Thus, if variable inductor 2 were 0f theordinary 'type providing an inductance variation of say"11, and 0 if thesignal 'collecting'sy'stm were expected to operate over arange or"frequencies "such as the broadcast range, which requires atotal inductance change or approximately 9, T it would only be possible tocover-this range if the loop induct 5 ance were not" larger" thanapproximately one fifth of the total inductance of the circuit 'atthehigh frequency end of the tuning range. A loop of such a low inductance;however, would notprovide a'n adequate-"amount of'signal interception tosecure satisfactory performance of thereceiver over thetotaltuningrange. 'Therefore in the construction of movable coretuned'.loopcircuits art was faced'with'the alternativeto either 5'0intercept an, adequate amount of signal "energy even" at the lowfrequency end of the range, and yetreta'in,coverage'of a'wvi'de "rangeof frequencies suchasthe broadcasflrange." Bearing in mind theinductance value that "loop'l is to have 5 for adequate interception,Iso' proportion'core portions 4 and w {relative to one another and-relativato winding"?- that movement of core structure 4 withTespect towinding 3 will produce such an inductance change as will varythe 0 totalinductance'of circuit'l 2 and 5 to therequired degree, in'spite' of therange re'ducing ef- 'fect" of the loop inductance. Forinstance, byconstructing my variable inductor 2"to'provide a ratio-of inductancevariationof, say, 33 my 5 1oop"n 1a yhave3 times-as much inductance'asmy variable inductorjf'atithe high end of the ifrequency range;thusprovidin'gior an adequate amountoi signal voltage to beintercepted,' and yetthe systemm y readily be tuned over a range ohaswideasjthe broadcastrange.

tion I ma'y so construct my antennasystem'lth'at whatever signal voltageIain able to supply'to ;th e;gr-id of the first tubeat theghighjrequenc5 end-may be maintainedsubstantiallyindependrifice; range coverage inorder to secure greatent of frequency over the total range of operation, in spite ofthe inherent characteristic; of

loops to receive signals of a lower'frequen'cy with lesser power thansignals of a higher frequency.

In order to compensate for this inherent nonuniformity ofloops'Ico'nstruct variable inductor 2 in such a manner that the gain ofmy signal'collecting system will vary inversely'as the frequency. Insignal collecting systems, the

gain is a function of the Q or of the circuit, and by proper choice ofthe permeability of core portion 4a "and of its loss characteristics,and by proper choice of thewall thickness of tube 4b and the dimensionsof both core portions relative to one another and relative to winding 3and the frequency range 'to be covered, I may construct these coreportions to produce such a change of the 'circuitresistance relative tothe change in circuit inductance I and circuitfrequency that theexpression varies inversely as the frequency; For this purpose I mayconstruct the-conductive core portion from a blend of metallic powdersof. different conductivity and I may. vary the character. of the'blendlengthwise in the core so as to give Also I may employ a blend ofmagnetic and non-magnetic metal powders for parts of my.,

core structure.

In a practical embodiment of the present-in vention constructed inaccordance'with Fig. 1 the signal collecting system was tunable over arange of frequencies from 1560 to540 kc. Loop l'had 13 turns of wire No.20/44 S. S. E. 7 inches high and 7 /2-incheswide, the length :of theWinding space being 2 -inches. The calculated inductance. of this loopwas 65 H.

Winding 3 was of the typeknown as progressive universal winding and waswound with wire No. 7/44 S. S. E. over a length of l%-inches on a coilform having an outer diameter of -.221- inch. Its inductance in air was52.3 [LI-I.

it predeterminedly'varying loss characteristics.

Portion 4a of core structure-4 was L e-inches long and had an outerdiameter ,of 2-inch. It

was made of a finely divided tin-iron alloy coninch. Its length was1%inches.- Whencom pletely within winding-3 it'decreased the induct-.ance of said winding from 52.3 H to 20 H.

Condenser!) had a capacitance of 123 ,UJLF which tuned circuit l 2 and 5to a frequency of 1560 kc. with copper tube 4b 'completely'withinwinding 3. The total resistance of the circuit at this frequency was23.8 ohms. Hence the Q or of the circuit was 35 at the upper end of thefrequency range. 'With the core moved so that core portion 4a wascompletely within'winding 3, the inductance of inductor Zhad r-isen'to'640 of the circuit was 26.4 ohms andthe effective Q of theztotalcircuit therefore was 91.2 at the low end of. the ifrequency'range.Thus, as the circuit was tunedfrom 1560 kc.to 540 kc.'its Q value hadincreased from 35 to 91.2. Therefore while.

the energy intercepted-by the loop had dropped to h of its originalvalue the gain of .the circuitfhad increased byfa factor cit- 2.61. withthe result that the voltage applied =to1'the grid of the first" tube hademainedsubstantially constant.

A The following practical; data (were obtained from the embodiment ofthe invention described above.

Grid gain Frequency ratio cast range;

By-grid. gain ratio-I" means the ratio'of the output voltage of thesystem measured in microvolts to the field strength measured-inmicro-volts. per meter that existed at the pointof interception andwhich had been adjusted to a substantially constant value throughoutthezrangex.

The above data show that the voltagesup plied to the gridof the-firsttube .had remained substantially constant .over the frequency rangecovered inspite of the "inherentcharacteristic of the 'loop. to receivesignals of a lower fre-i quency with =lesser1pow'er than signals of ahigher frequency; i Still greater frequency independence of .thevoltagesupplied by the loop circuit to the grid of the first' tube maybe 'obtained, forv instance;

by core portion 41)- being constructedas of var-i9 Q able wallfthickness or of variable shape. Also core p or'tion 4a may beconstructed to havevari able loss-characteristics withrthe end enteringthe windingli first being preferably constructed to have relativelyhigherllosses per unit volume than other parts thereof (measured at thesame frequency); Likewise core member 4b may be constructed from anumber of'metals of diiferent electrical conductivity; -Moreover the twocore members maybe constructed to. partly overlap one another at theirjunction in 'a manner similar to'that indicatedin Fig. 2. I While Ihave-"explained' my invention with the aidbf a particular embodimentthereof, it will be understood thatI do not limit myself thereto. Thus,the present invention may be used in signal co11ecting'syster'ns otherthan the one specifically illustrated and ov er ranges other than thebroad- Having thus described my invention WhatI claimis z' r a c 1.'Animproved resonant circuit and tuning means "of the class, includinganunexposed'in ductive'winding'," a fixed tuning capacitor, and a corestructure movabl e relatively to said unexposed'induetive' element tochange'the inductance of'the resonanti circuit .to tune it throughout iaband of frequencies, said core structure including ,uH; The circuit thenresonated at a'frequency of 540 kc. .At this frequency the totalresistance:

two; portions in endito end relationship; a first oi'i'saidacoreportions being-'magnetic andrvarying the inductanceaof saidiunexposedinductive windsv ingifrom substantially the amount due to-unitypermeability or an airmagnetic path toa substantially larger and maximuminductance value due,

posed inductive winding; said improvedltuning means including atwo partcorejconstruction of the class above describedin which the'magnetic corepart comprises comm'inuted ferromagnetic particles closely associated insolid form and havinga; high effective permeability when fully insertedinto said unexposed inductive winding e and capable unaided of tuningsaid resonant circui't over at leasttwo-thirds of said frequencybandfrom the low frequency end thereof, and

' the non-magnetic and electrically conductive core pa'r't comprises atube of metal'of good electrical conductivity and having a thin walllimiting. the maximuminductance-reducing eifect thereof in such mannerthat said'non' magnetic core part will unaidedtunesaid resonantcircuitover not morethan one third of'said frequency'band from theihighfrequency endthereof.

V2:-An"improved resonant circuit andtuning means of thezclass' including'anunexposed inductive windingafixed tuning capacitor, and a corestructure movable relatively to' said unexposed inductive element tochange the inductance of the resonant circuit to tune it'throughout abandof frequencies, said core'structure including two:portions inend toend relationship, a-first of said core portionsbeing magnetic andvarying the inductance of said unexposed inductive winding'i'romsubstantially the amount due to unity permeability of anrair magneticpath to a -substantially larger and maximum inductance value duelto thegreateriefiective permeability of said magneticportion, and :the otherof said coreportions being non-magnetic andof electrically conductivematerial acting .to' reduce the inductance ofisaid unexposed inductivewinding below its inductance resulting from unitipermeabilityof itsmagnetiopath depending upon theposition oi. said: other core portionrelatively to saidunexposed inductive winding, which improved resonant'circuit includesin serieswith said unexposed inductive..- winding, anexposed inductive element having an airpathinductance at least as greatas the air path inductance otthelfliexposed inductive winding, saidimproved tuning means including a two'part core-construction of theclass above described in which the magnetic' core part comprisescomminuted ferromagnetic particles closely associated in solid form andhav-, ing a'higheffective permeability when fully insorted, :into: saidunexposed; inductivewinding and 'capable unaidedcf; tuningsaid resonantcircuit .over at least two-thirds of said frequency band jromrthe'lowfrequency end thereof, and -the:non'-magnetic and electricallyconductive core partucomprises a tubeof; metal "of good electricalconductivity and having a thin wall limiting the.

maximum;inductance-reducing effect thereof in such manner-that said'non-magnetic-core part will unaided tune. said resonant circuit overnotmore than one thirdof said frequency band from the highfrequency-endthereofgsaid core con-' struction having such dimensionsandsuch dis-, tribution, of eifective permeability and effectiveresistance relatively to the-form,,size and inductance of said unexposedinductive winding as to vary the ratio coL MY 7, of the resonant circuitsubstantially inversely as the tuned frequency throughout the tuningband.

3. An improved resonant circuit and tuning means of the class includingan unexposed inductive winding, a fixed tuning capacitonand a corestructure movable relatively to said unexposed inductiveelement tochange the inductance of the resonant circuit totune-itthroughout a bandof frequencies, said core structure including two portions in end to endrelationship, a first of said core portions being magnetic and varyingthe inductance of said unexposed inductive winding from substantiallythe'amount due to unitypermeability of an air magnetic path to asubstantially larger and maximum inductance value due to the greatereffective permeability of said magnetic portion; and-the other of saidcore portions being non-magnetic and ofelectrically conductive materialacting to'reduce the inductance of said unexposed inductive windingbelow its inductance resulting from unit permeabilityofits magnetic pathdepending. upon the position of said other core portion. relatively-tosaid unexposed inductive winding; which improved resonanti circuitincludes in 'series with said unexposed inductive winding an exposedinductive element having anair pathinductanceat least as greatas theair'path. inductance of the unexposed inductive winding, said'improvedtuning means including a two part core construction of the class abovedescribedin which'the magnetic core part comprises comminutedferromagnetic particles closely associated in solidform and having ahigh effective permeability, when fully inserted into said unexposedinductivewinding and capable unaidedof tuning said resonant circuit overat least two-thirds of said frequency band from the low frequency endthereof, and the nonmag'netic'and electrically conductive core partcomprises a tube of metal of good electrical conductivity and havingathinrwall limiting the maximum-inductance-reducing efiect thereof insuch manner that said non-magnetic core-part will unaided tune saidresonant circuit overnot more than one. third of :said frequency bandfrom the high frequency end thereof, the effective permeability of saidmagnetic, core part, when fully inserted in said unexposed element beingat least of the order of ten, and the thickness of wall of saidnon-magnetic core part being of the order of one'sixty-fourth of aninch? 4. An improved resonant collector circuitand tuning means of theclassincluding a permeability tuning coil,.a fixed tuningcapacitorconnected with said coil, and a core structure movable into andfrom said coil to tune said resonant circuit throughout a band offrequencies, said corestructure including a magnetic portion and anon-magnetic and electrically conductive por tion connected in end toend relation, which improved resonant collector circuit, includes thecombination of a loop collector, a permeability tuning coil connected inseries with said. loop collector, said coil having an axial length'atleast three times its internal diameter and said loop collector havingan air path inductance at least as great as the air path inductance ofsaid coil, a fixed capacitor having its terminals connected around theseries related loop collector and coil, and a tuning means comprising acylindrical core portion-of powdered ferromagnetic material in solidform and a non-magnetic and electrically conductive tubular core portionaxially aligned with and connected end to end with said cylindrical coreportion, the external diameter of said tubular core portion beingsubstantially the same as the diameter of said cylindrical core portion,said cylindrical core portion having a high effective permeability whenfully inserted in said coil by which said cylindrical core portionunaided will tune said resonant circuit throughout at least two-thirdsof said frequency band from the low frequency end thereof, said tubularcore portion having a thin wall effecting the tuning of said resonantcircuit throughout not more than one-third of said frequency band fromthe high frequency end thereof, said two core portions being eachsubstantially'as long as the length of combination of a loop collector,a permeability tuning coil connected'in series with said loop collector,said coil having an axial length at least three times its internaldiameter and said loop collector having an air path inductance at leastas great as the air path inductance of said coil,

a fixed capacitor having its terminals connected around the seriesrelated loop collector and coil, and a tuning means comprising acylindrical core portion of powdered ferromagnetic material in solidform and a non-magnetic and electrically conductive tubular core portionaxially aligned with and connected end to end with said cylindrical coreportion, the external diameter of said I tubular core portion beingsubstantially the same as the diameter of said cylindrical core portion,said cylindrical core portionhaving a high effective permeability whenfully inserted in said coil by which said cylindrical core portionunaided will tune said resonant circuit throughoutat least two-thirds ofsaid frequency band from the low frequency end thereof, said tubularcore portion having a thin wall effecting the tuning of said resonantcircuit throughout not more than onethird of said frequency band fromthe high frequency end thereof, said two core portions being eachsubstantially as long as the length of said coil, said cylindrical coreportion havingfan effective permeability when fully inserted into saidcoil of at least the order of ten and said tubular core portion having awall thickness of the order of one sixty-fourth of an inch.

i 6. An improved resonant collector c-lrcuit'and tuning means of theclass including a permeability tuning coil, a fixedtuning capacitorconnected withsaid coil,"'and a core structure movable into and fromsaid coil to tune said resonant circuit throughout a band offrequencies, said core structure including a magnetic portion and anon-magnetic and electrically conductive portion connected in end to endrelation, which improved resonant collector circuit includes thecombination of a loop. collector, a permeability tuning coil connectedin serieswith said loop collector, said coilhaving an axiallength atleast three times its internal diameter and said loop collector havingan air path inductance atleast as-great-as the air path inductance of"saidcoil, a

. fixed capacitor having its terminals connected around the seriesrelatedloop collector and coil, and a tuning means comprising acylindrical core portion of powdered ferromagnetic material in solidform and a non-magnetic and electrically conductive tubular core portionaxially aligned I with and connected end to endwith said cylin-' dricalcore portion, the external diameter of said tubular core portion beingsubstantially the same as the diameter of said cylindrical core portion,said cylindrical core portion having a high effective permeability whenfully inserted in said coil by which said cylindrical core portionunaided will tune said resonant circuit throughout at least two-thirdsof said frequency band from the low frequency end thereof,-said tubularcore portion having a-thin wall effecting the tuning of said resonantcircuit throughout not more than one-third of said frequency. band fromthe high frequency end thereof, said two core portions being eachsubstantiallyaslong as thelength of saidcoil, said core portions havingsuch dimen-' sions, proportions andcompositions relatively to the form,size and inductance of said coil as to vary the ratio of the resonantcircuit substantially inversely as i the tuned frequency throughout thetuning band.

7. A signal collecting system for radio receivers and the like includingan' exposed inductive element, an unexposed inductive element, and acapacitance connectedto form a resonant circuit,,said unexposedinductive element comprising a winding and a core structure having firstand second portions arrangeden'd to end for successive movement into andfrom said winding,

' said first core portion comprising a ferromagnetic body of comminutedmagnetic material in cylindrical-form and said-second core portioncomprising a thin walled'non-magnetic tube of 'good electricalconductivity, the materials of said core portions and their proportionsrelatively to each other and to the inductance of said winding beingsuch as to vary the ratio WILLIAM A; SCI-IAPER.

